Microwavable package

ABSTRACT

The disclosed invention provides a microwavable package for a food product. The package comprises a base with an active microwave energy heating element to support the food product. The active microwave heating element comprises energy collecting resonant loops, tuned structures, and transmission lines to collect incident microwave energy and redirect it to other parts of the food product. The microwave package also includes a cover comprising a microwave energy interactive layer including one or more apertures within the cover. The apertures promote localized fields to promote browning of the food product in the local areas around the apertures. The cover may also comprise a susceptor layer that is heated in localized areas around the apertures due to the fields promoted by the apertures and impingement by incident microwaves energy through the apertures, thereby providing localized browning of the food product.

This application is a continuation of U.S. application Ser. No.08/703,098, filed Aug. 16, 1996 now abandoned and is the National Phase(371) and PCT/CA97/00597 filed Aug. 26, 1997.

FIELD OF THE INVENTION

The present invention relates to packages for food products and inparticular to a microwavable package and an active microwave energyheating element for the same.

BACKGROUND OF THE INVENTION

Microwave ovens have become a principle form of cooking food in a rapidand effective manner and the number of food products available forpreparation in a microwave oven is constantly increasing. As the marketfor microwavable food products has increased, so the sophisticationrequired from such food products has also increased. There is,therefore, a continuing demand to improve the quality of food preparedin a microwave oven and to ensure that when it is presented to theconsumer, the food product is attractive and meets the standardsnormally associated with such food.

Foods that are specially prepared for cooking within a microwave ovenare delivered to the consumer in containers that may be used directlywithin the microwave oven to facilitate preparation, These containersmust therefore not only be capable of containing the food product duringtransport in an effective manner but must also be capable ofcontributing to the cooking of the food product within the microwaveoven and the subsequent presentation of the food product.

As the demand for more sophisticated food products increases, so thedemand for effects, particularly appearance, normally associated withfood preparation also increases. For example, it is desirable for a foodproduct that includes a pastry shell or lid to have a brownedappearance, so that it appears to have been baked. While these effectscan be produced in isolation, it becomes more difficult to produce suchan effect in combination with a container that can also uniformly heatthe food product within a time that offers advantages over conventionalcooking techniques.

Typically, the areas in which browning or crisping are required arethose on the outer surfaces of the food product. Those areas typicallyreceive the highest proportion of incident microwave radiation andtherefore cook or heat the quickest even though the power distributionis very non-uniform over these surfaces. On the other hand, there areareas of the food product that are relatively shielded from incidentmicrowave radiation or exist in a region of a minimum RF field and whichtherefore require longer cooking periods. If, however, a longer cookingperiod is provided, the outer surfaces of the food product tend to charand burn, leading to an unacceptable food product.

Various attempts have been made in the past to provide containers thatwill produce effects normally associated with cooked foods. For example,U.S. Pat. No. 5,322,984 to Habeger, Jr. Et al. and assigned to The JamesRiver Corporation suggests a container having heating devices on thebottom wall and possibly the top wall of the container. The heatingdevices are designed to provide a charring effect normally associatedwith barbecuing by directing energy normally not incident upon the foodproduct into specific regions. This is purported to produce a localisedcharring of the food product. Overall, however, such containers have notbeen successful. The charring effect produced on the food product may beattributed to the high field intensities and associated induced currentsthat result from the concentration of energy at particular locations. Inpractice it is found that those induced currents may also cause charringand burning of the container itself.

U.S. Pat. No. 4,927,991 to Wendt et al and assigned to The PillsburyCompany discloses a microwavable package for foodstuffs and inparticular pizza. The package includes a tray on which a grid incombination with a susceptor are located. The grid and susceptorcombination act together as a microwave energy heating element. Thepackage also includes an aluminum top having apertures provided in it.The apertures allow microwave energy to penetrate the top thereby toheat the foodstuff.

It has also been found that in order to produce the required results forthe preparation of the food product, the container must be capable ofcontrolling distribution of energy about the food product, to utilizethe energy in the most efficient manner, and at the same time ensurethat the food product and the container provide a pleasant andacceptable finished product. Also, the containers must be able to holdthe food product securely to avoid damage to the food product duringtransport. It has been found that in the case of pizza containers,conventional designs have not been adequate resulting in separationbetween the pizza crust and the toppings during transport.

It is therefore an object of the present invention to provide a novelfood product package and active element for the same which obviates ormitigates at least one of the above disadvantages.

SUMMARY OF THE INVENTION

According to one aspect of the present invention there is provided amicrowavable package comprising:

a base to support a food product;

an active microwave energy heating element on said base to effectheating of a food product upon impingement by microwave energy; and

a cover spaced from said active microwave energy heating element tooverlie said food product, said cover including a microwave energyinteractive material layer extending substantially over said foodproduct, and a plurality of apertures in said microwave energyinteractive material spaced about a peripheral margin of said cover,said apertures being sized to promote localised fields to promotebrowning of said food product.

In one embodiment, the apertures are in the form of elongate slotsarranged in concentric rings. Microwave energy interactive materialislands may be located within the slots to enhance further the cookingperformance. In this embodiment, the active microwave energy heatingelement includes a plurality of energy collecting structures, eachenergy collecting structure having resonant loops. The resonant loopshave a perimeter sufficient to limit currents induced therein to below apredetermined level upon impingement by incident microwave energy. Theenergy collecting structures distribute energy towards a central regionof the food product to heat the food product generally uniformly and toinhibit charring of the base. In one form, the active microwave energyheating element further includes tuned structures at spaced locationseach of which is located between a pair of the resonant loops.

According to another aspect of the present invention there is provided amicrowavable package comprising:

a base to support a food product;

an active microwave energy heating element interposed between said foodproduct and said base to effect heating of said food product uponimpingement by microwave energy; and

a cover spaced from said active microwave energy heating element tooverlie said food product, said cover including a substrate andmicrowave energy interactive material on said substrate to cover atleast a portion of said food product, said substrate extending beyondthe peripheral edge of said microwave energy interactive material toisolate electrically said base and said cover.

According to still yet another aspect of the present invention there isprovided a packaged food product comprising:

a base to support said food product;

a flexible cover to overlie and conform to said food product; and

a flexible wrap to constrain said base and cover and inhibit relativemovement therebetween.

According to still yet another aspect of the present invention there isprovided an active microwave energy heating element for a microwavablepackage to heat generally uniformly a food product within said package,said active microwave energy heating element comprising:

a plurality of energy collecting structures, each of said energycollecting structures including resonant loops having a perimetersufficient to limit currents induced therein to below a predeterminedlevel upon impingement by incident microwave energy; and

a plurality of tuned structures at spaced locations and positionedbetween adjacent resonant loops, said energy collecting and tunedstructures distributing energy across said active microwave energyheating element to heat generally uniformly said food product andinhibiting charring of said microwavable package.

In still yet another aspect of the present invention there is provided amicrowavable package comprising:

a tray having a base and an active microwave energy heating element onsaid base to effect heating of a food product on said tray uponimpingement by microwave energy; and

a plurality of spaced apertures in said tray to permit moisture releasedfrom a food product to pass through said tray.

The present invention provides advantages in that the microwavablepackage design is such to heat generally uniformly the food productwhile browning the outer periphery of the food product. This design isparticularly suited to cooking pizzas.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described more fullywith reference to the accompanying drawings in which:

FIG. 1 is an exploded side elevational view of a microwavable package inaccordance with the present invention;

FIG. 2 is a top plan view of a tray having an active microwave energyheating element thereon for the microwavable package of FIG. 1;

FIG. 3 is cross-sectional view of FIG. 2 taken along line 3—3;

FIG. 4 is a top plan view of a cover forming part of the microwavablepackage of FIG. 1;

FIG. 5 is a cross-sectional view of FIG. 4 taken along line 5—5;

FIG. 6 is a top plan view of an alternative embodiment of a cover for amicrowavable package in accordance with the present invention;

FIG. 7 is an enlarged part cross-sectional view of FIG. 6 taken alongline 7—7;

FIG. 8 is an enlarged top plan view of a portion of FIG. 6;

FIG. 9 is a top plan view of yet another alternative embodiment of acover for a microwavable package in accordance with the presentinvention;

FIG. 10 is a top plan view of an alternative embodiment of a tray havingan active microwave energy heating element thereon for a microwavablepackage in accordance with the present invention;

FIG. 11 is a top plan view of another alternative embodiment of a trayhaving an active microwave energy heating element thereon for amicrowavable package in accordance with the present invention;

FIG. 12 is a top plan view of yet another alternative embodiment of atray having an active microwave energy heating element thereon for amicrowavable package in accordance with the present invention;

FIG. 13a is a top plan view of still yet another alternative embodimentof a tray having an active microwave energy heating element thereon fora microwavable package in accordance with the present invention; and

FIG. 13b is a cross-sectional view of FIG. 13a.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 1, a microwavable package for a food product isshown and is generally indicated to by reference numeral 10. The package10 in this particular example is best suited to contain uncooked pizzashaving raw dough crusts.

As can be seen, in this particular example the package 10 includes atray 11 having a base 12 formed of suitable material such as forexample, paperboard. The base is in the form of a circular disc sized tothe dimension of the food product to be held in the package 10. The basecan of course take other geometric shapes if desired. An activemicrowave energy heating element 14 is bonded or adhered to one surfaceof the base 12. The food product, in this case a pizza 16, contacts themicrowave energy heating element and is supported by the base 12. Aflexible cover 18 overlies the top of the food product 16 and conformswith its surface. The cover 18 can be folded at its periphery to overlieat least part of the sides of the food product. A plastic wrap 20encompasses the base 12, cover 18 and food product 16 to maintain thebase 12 and cover 18 in secure contact with the food product 16 andinhibit relative movement therebetween.

Referring now to FIGS. 2 and 3, the active microwave energy heatingelement 14 is better illustrated. As is shown, the microwave energyheating element 14 is in the form of a laminate 30 and includes asubstrate 32 formed of suitable material such as for example paper,paperboard or polymeric film. One surface 32 a of the substrate isadhered to the base 12 and an opposed surface 32 b has a pattern 34 ofmicrowave interactive material deposited thereon. The microwave energyinteractive material 34 may be electroconductive or semiconductivematerial such as metal foil, vacuum deposited metal or metallic ink. Theelectroconductive material is preferably aluminum although other metalssuch as copper may be employed. In addition, the electroconductivematerial may be replaced with a suitable electroconductive,semiconductive or non-conductive artificial dielectric or ferroelectric.Artificial dielectrics comprise conductive subdivided material in apolymeric or other suitable matrix or binder and may include flakes ofelectroconductive metal such as aluminum.

A susceptor 36 including at least one layer of suscepting materialcovers the microwave energy interactive material 34 and the substrate 32and produces a heating effect upon excitation by incident microwaveenergy as is well known. The susceptor 36 may be in the form of aprinted ink or alternatively, a coating sputtered or evaporated over theactive element 14. The susceptor 36 may not be utilized or additionallayers of suscepting material may be provided depending on the heatingeffect required.

The pattern of microwave energy interactive material 34 and susceptor 36constitute a microwave energy controlling structure which permits acontrolled degree of penetration of incident microwave energy throughthe base 12 and channels microwave energy towards a central region ofthe food product. Specifically, the design of the active microwaveenergy heating element 14 moderates penetration of microwave energy inthe peripheral region of the food product 16 and directs microwaveenergy towards its central region. This allows the food product to cookmore uniformly.

Looking at the pattern of microwave energy interactive material 34 moreclosely, it can be seen that the pattern includes a plurality ofcircumferentially spaced transmission elements 40 arranged in a ringabout a circular island 42 positioned at the center of the microwaveenergy heating element 14. Each transmission element 40 includes a pairof resonant loops 44 interconnected by a pair of transmission lines 46.In this particular example, the loops 44 are generally circular. Theloops 44 have a perimeter sufficient to limit currents induced thereinto below a predetermined level and which is as close to an integermultiple of the effective wavelength of the incident microwave energy.

The loops 44 are tuned to collect microwave energy from the peripheralregion of the microwave energy heating element 14 and distribute theenergy to a central region of the food product to heat the food productgenerally uniformly and to inhibit charring of the base 12. Thetransmission lines 46 are selected to provide a progressive power lossfrom each of the tuned loops 44 and are of such length that the powerdecays towards zero at the mid-point of the transmission lines. This isachieved by matching the energy fed by the loops 44 to the absorptioncharacteristics of the transmission lines 46.

Two arrays 50 and 52 of tuned structures 54 and 56 respectively are alsocircumferentially spaced in a ring about the circular island 42. Thetuned structures 54 of array 50 are positioned between adjacenttransmission elements 40 while the tuned structures 56 of the array 52are positioned between the two loops 44 of each transmission element 40.The tuned structures 54 and 56 each include nested loops and islands aswill now be described.

Each tuned structure 54 and 56 includes a deltoid ring 60 having roundedcorners. Within the deltoid ring 60 is an annular ring 62 joined toopposed corners of the deltoid ring by a pair of bridges 64. A circularisland 66 is positioned within the annular ring 62. A sagittal island 68is also positioned within the deltoid ring 60. The arrowhead 70 of thesagittal island 68 points toward the center of the microwave energyheating element 14. The shaft 72 of the sagittal island 68 extendsradially from the arrowhead 70 crossing the annular ring 62 andterminating at the circular island 66.

The deltoid rings 60 of the tuned structures 54 are more elongate thanthe deltoid rings of the other tuned structures 56 and therefore aremore pointed towards the center of the microwave energy heating element14. The arrowheads 70 of the sagittal islands 68 within the deltoidrings 60 of the tuned structures 54 are also more pointed than thearrowheads of the tuned structures 56. As a general principle, the loopsand islands are reactive with the incident microwave energy and so thenature and extent of their coverage of the microwave energy heatingelement determines the amount and distribution of microwave energy. Theradial spacing between the deltoid and annular rings is such that theenclosed circuit length is close to λ where λ is equal to the effectivewavelength of the incident microwave energy. The islands principallyinhibit transmission of microwave energy but provide a local excitationat their outer edges.

The outer-most corners of the deltoid rings 60 are joined to an outerring 76 which covers the peripheral margin of the microwave energyheating element 14 by bridges 74. The bridges 64 and 74 permit the tunedstructures 54 and 56 to be excited by the antenna formed by the innercircumference of peripheral edge 76 b.

The outer ring 76 has a circular outer peripheral edge 76 a and anundulating inner peripheral edge 76 b. Two concentric rings ofcircumferentially spaced apertures 78 are formed in the outer ring. Theapertures 78 are in the form of elongate slots having cambered majoredges. In the specific embodiment shown, the elongate slots 78 of thetwo rows are staggered.

Referring now to FIGS. 4 and 5, the cover 18 is better illustrated. Thecircular cover 18 is also in the form of a laminate 80 and includes asubstrate 82 formed of suitable material such as for example, paper,paperboard or a polymeric film. Microwave energy interactive material 84of one of the types previously described is on one surface of thesubstrate 82. A susceptor 86 including at least one layer of susceptingmaterial overlies the microwave energy interactive material 84 and thesubstrate 82 although the susceptor 86 is optional. The substrate 82extends beyond the peripheral edge of the microwave energy interactivematerial 84 to ensure that the cover 18 and the microwave energy heatingelement 14 remain electrically isolated if the edge of the cover 18contacts the microwave energy heating element. Spaced apertures 88 areformed in the microwave energy interactive material 84 about itsperipheral margin. The apertures 88 are in the form of elongate slotshaving cambered major edges. In the particular example shown, the slotsare arranged in three concentric rings with the slots in the variousrings being staggered. The elongate slots 88 are sized to promotelocalized fields to enhance the susceptor 86 and promote browning of thefood product 16 when penetrated by microwave energy. In addition, thecircumference of the shielding may be designed to enhance or limit theelectrical activity at its edge.

During packaging, the food product 16 is placed on the microwave energyheating element 14 and is supported by the base 12. The flexible cover18 is then placed over top the food product 16 with the susceptor 86 incontact with the food product. Since the cover 18 is flexible itgenerally conforms to the shape of the food product. Following this, thebase 12, cover 18 and food product 16 are shrink wrapped with theplastic film 20 to hold securely the food product 16 between the base 12and the cover 18 and inhibit relative movement between them. Because thewrap 20 holds the cover, base and food product securely, in the case ofpizzas, separation between the crust and the pizza toppings is unlikelyto occur.

When the food product 16 is to be cooked, the wrap 20 is removed and thefood product 16 is placed in the microwave oven supported by the base 12and with the cover 18 overlying the top of the food product. The outeredge of the cover 18 is preferably folded down over at least a portionof the sidewall of the food product to provide some edge heating. Thedesign of the microwave energy heating element 14 and cover 18 are suchto heat uniformly the food product 16 while ensuring that the crust ofthe food product is cooked and browned.

Although the cover 18 is shown as being circular and planar, the covercan take other geometric shapes and may be in the form of a dome tooverlie the top of the food product 16 as well as its sides.

Referring now to FIGS. 7 and 8, another embodiment of a cover for amicrowavable package is shown. In this embodiment, two concentric ringsof apertures 188 are formed in the peripheral margin of the microwaveenergy interactive material 184. The apertures in this case arerectangular in appearance and have rounded corners. Islands 100 arelocated within each aperture 188. Each island 100 itself has a flatteneddecussate aperture 102 formed in it.

Although, the cover 18 has been described as being flexible to allow itto be folded over at least a portion of the sides of the food product16, those of skill in the art will appreciate that the peripheral marginof the base 12 may also be made to be flexible so that the activemicrowave energy heating element 14 may be folded over at least aportion of the side of the food product together with or instead of thecover 18. In these instances, the cover 18 and base 12 should bedimensioned to inhibit electrical coupling of the microwave energyinteractive material on the cover and base.

In addition, although the microwave energy heating element and coverhave been described as a laminate with the microwave energy interactivematerial deposited on one surface of the substrate and covered by asusceptor, it should be realized that the pattern of microwave energyinteractive material can be deposited on one surface of the substrateand the susceptor can be deposited on an opposite surface of thesubstrate. In this case, the surface of the substrate on which themicrowave energy interactive material is deposited, is bonded or adheredto the base 12.

Referring now to FIG. 9, yet another embodiment of a cover 218 for amicrowavable package is shown. In this embodiment, three concentricrings of apertures 288 are formed about the peripheral margin of themicrowave energy interactive material 284. The apertures 288 are in theform of elongate slots and are arranged so that the apertures of thevarious rings are staggered. Within the inner most ring of apertures288, is an array of additional apertures 300. The apertures 300 are inthe form of elongate slots and are arranged in two alternating patterns302, 304 about the center of the cover 218. Each pattern 302 ofapertures 300 includes three radially directed apertures arranged toform a triangle with a tangentially oriented aperture between the inneraperture and the two outer apertures. The apertures that are arranged toform a triangle taper in width towards the center of the cover 218. Eachpattern 304 of apertures 300 includes an outer tangentially orientedaperture and an inner radially directed aperture 300. The radiallydirected aperture has cambered major edges. An annular aperture 308 isformed at the center of the cover and surrounds a circular island 310.

Depending upon the depth of the crust, the toppings appearance anddesign on the crust and the size of the pizza, a cover of the typesillustrated may or may not be used. Although the cover will assistheating of the food product, due to cost in many applications, atransparent cover or no cover will be used.

Although FIGS. 4, 6 and 9 illustrate different embodiments of the cover,those of skill in the art will appreciate that other configurations ofmicrowave energy interactive material on the cover can be used. Forexample, the cover may include islands of microwave energy interactivematerial in the shape of circles or polygons. Alternatively, themicrowave energy interactive material may include annular or polygonalloops surrounding correspondingly shaped islands.

Referring now to FIG. 10, another embodiment of a tray 411 is shown. Inthis embodiment, the configuration of the tuned structures 450 and 452and the outer peripheral ring 476 is different from that of FIG. 2. Ascan be seen, each tuned structure 450 and 452 includes a generallycircular loop 480 joined to the outer ring 476 by a bridge 474. The loop480 is connected to a triangular island 482 by way of a pair oftransmission lines 484. Nested loops 486 are positioned between thetransmission lines 484 adjacent the triangular islands 482 and includean annular ring 488 surrounding a circular island 490. The triangularislands 482 of the tuned structures 450 are longer than those of tunedstructures 452 and point towards a circular island 492 at the center ofthe tray. Three concentric rings of apertures 496 are provided throughthe tray 411. The apertures 496 allow moisture released from the foodproduct during cooking to pass through the tray 411. In use, a moistureabsorbing towel or the like will typically be placed beneath the tray toabsorb moisture passing through the apertures 496. The substrate 430extends beyond the peripheral edge of the active heating element 414.

Referring now to FIG. 11, another embodiment of a tray 511 is shown.Tray 511 is very similar to that shown in FIG. 2. As can be seen, theactive microwave energy heating element 514 includes a plurality ofcircumferentially spaced transmission elements 540 arranged in a ringabout the center of the tray. An array of tuned structures 550 and 552are also circumferentially spaced in a ring about the center of thetray. Tuned structures 550 are positioned between adjacent transmissionelements 540 while tuned structures 552 are positioned between the loops544 of each transmission element 540. In this case, the tuned structures550 and 552 are the same. Unlike the embodiment of FIG. 2, the tray 511does not include an island at its center. However, the transmissionlines 546 are longer and extend closer to the center of the tray. Theloops 544 are generally diamond-shaped with rounded corners and thetuned structures 550 and 552 are more elongate and have sharper corners.Also, the substrate 530 extends beyond the peripheral edge of the activeheating element 514.

FIG. 12 shows yet another embodiment of a tray 611. In this embodiment,the transmission lines 646 extend closer to the center of the trayobviating the need for an island at the center. Also, a bridge 680 joinsthe transmission lines 646 of each transmission element 640 at theirmid-point. The tuned structures 650 and 652 are the same and are in theform of loops resembling arrowheads. The tuned structures 650 and 652are joined to the outer ring 676 by bridges 674.

Referring now to FIGS. 13a and 13 b, yet another embodiment of a tray711 is shown. In this embodiment, tray 711 includes a base 712, andupstanding sidewall 713 about the periphery of the base 712 and aperipheral rim 715 about the sidewall. The active heating element 714extends over the base and the sidewall 713. The transmission elements740 and tuned structures 750 and 752 are on the base 712 while the outerring 776 runs about the periphery of the base and over the sidewall 713.As can be seen, similar to the previous embodiment, bridges 780 join thetransmission lines 746 at their mid-points. The tuned structures 750 and752 are the same and are in the form of diamond-shaped loops 782 joinedto the outer ring 776 by narrow bridges 774. A triangular projection 784extends into each loop 782. A ring of apertures 778 is formed in theouter ring 776 about the periphery of the base. A ring of apertures 788similar to those provided in the cover of FIG. 6 are formed in the outerring about the circumference of the sidewall.

In each of the embodiments of FIGS. 10 to 13 b and similar to theembodiment of FIG. 2, the active microwave heating element on the traycollects microwave energy from the periphery of the tray and dissipatesit progressively towards the center of the tray to provide a uniformheating effect.

While the above described embodiments show a tray and cover separatefrom the tray, the active microwave energy heating elements may beprovided on opposed surfaces of a bag or pouch designed to accommodatethe food product.

Although particular embodiments of the microwave energy heating element14 have been described and shown it should be apparent to those of skillin the art that other patterns of microwave energy interactive materialmay be provided on the microwave energy heating element to achieve thedesired uniform heating of the food product. Examples of alternativepatterns of microwave energy interactive material designed to heatuniformly a food product upon exposure to incident microwave energy canbe found in applicant's co-pending application filed on Sep. 18, 1995and issued serial number 08/529,450.

Also, although the tray 411 has been shown to include apertures 496therein to allow moisture to pass through the tray, those of skill inthe art will appreciate that the other embodiments of the trays may alsoinclude apertures. In addition, apertures may be provided through thecovers if desired to allow moisture to pass.

Those of skill in the art will also appreciate that variations andmodifications may be made to the present invention without departingfrom the spirit and scope thereof as defined by the appended claims.

What is claimed is:
 1. A microwavable package comprising: a base tosupport a food product; an active microwave energy heating element onsaid base to effect heating of a food product upon impingement bymicrowave energy; and a cover spaced apart from said active microwaveenergy heating element to overlie said food product, said coverincluding a microwave energy interactive material layer extendingsubstantially over said food product, said microwave energy interactivematerial including a plurality of apertures spaced about said cover,said apertures being sized to promote localized fields to promotebrowning of said food product.
 2. A microwavable package as defined inclaim 1 wherein said apertures are in the form of elongate slots.
 3. Amicrowavable package as defined in claim 2 wherein said elongate slotsare arranged in concentric rings.
 4. A microwavable package as definedin claim 3 wherein said rings are circular.
 5. A microwavable package asdefined in claim 4 wherein the slots in said concentric rings arestaggered.
 6. A microwavable package as defined in claim 5 furtherincluding at least one layer of suscepting material on said cover andoverlying said microwave energy interactive material.
 7. A microwavablepackage as defined in claim 2 wherein microwave energy interactivematerial islands are located within said elongate slots.
 8. Amicrowavable package as defined in claim 7 wherein said elongate slotsare arranged in concentric rings.
 9. A microwavable package as definedin claim 8 wherein said rings are circular.
 10. A microwavable packageas defined in claim 9 wherein the slots in said concentric rings arestaggered.
 11. A microwavable package as defined in claim 7 wherein eachof said microwave energy interactive material islands has an apertureformed therein.
 12. A microwavable package as defined in claim 11wherein said apertures are substantially decussate.
 13. A microwavablepackage as defined in claim 1 wherein said active microwave energyheating element includes a plurality of energy collecting structures,each of said energy collecting structures including resonant loopshaving a perimeter sufficient to limit currents induced therein to belowa predetermined level upon impingement by incident microwave energy,said energy collecting structures distributing energy towards a centralregion of said food product to uniformly heat said food product and toinhibit charring of said base.
 14. A microwave package as defined inclaim 13 wherein said energy collecting structures include a pair ofresonant loops interconnected by transmission lines, said transmissionlines configured to provide a progressive power loss between saidresonant loops.
 15. A microwavable package as defined in claim 14wherein the perimeter of said resonant loops and the length of each ofsaid transmission lines are substantially equal to an integer multipleof the effective wavelength of said incident microwave energy projectedonto said microwave energy heating element.
 16. A microwavable packageas defined in claim 15 wherein said resonant loops are circular.
 17. Amicrowavable package as defined in claim 16 wherein said energycollecting structures are circumferentially spaced and arranged in aring about the center of said active element.
 18. A microwavable packageas defined in claim 17 wherein said active microwave energy heatingelement further includes a plurality of tuned structures at spacedlocations and positioned between adjacent resonant loops.
 19. Amicrowavable package as defined in claim 18 wherein said tunedstructures include nested loops.
 20. A microwavable package as definedin claim 19 wherein said nested loops are joined by bridges.
 21. Amicrowavable package as defined in claim 1 further including a pluralityof spaced apertures provided through said base and active microwaveenergy heating element to allow moisture released from said food productto pass.
 22. A microwavable package as defined in claim 21 wherein saidapertures are arranged in concentric rings.
 23. A microwavable packagecomprising: a base to support a food product; an active microwave energyheating element interposed between said food product and said base toeffect heating of said food product upon impingement by microwaveenergy; a cover spaced apart from said active microwave energy heatingelement to overlie said food product, said cover comprising: microwaveenergy interactive material covering at least a portion of said foodproduct, said microwave energy interactive material containing aplurality of apertures spaced about said cover; a substrate supportingand extending beyond the peripheral edge of said microwave energyinteractive material to isolate electrically said base and said cover;and at least one layer of suscepting material interposed between saidfood product and said microwave energy interactive material; whereinsaid apertures are sized to promote a localized fields to locallyenhance said at least one layer of suscepting material and promotebrowning of said food product.
 24. A microwavable package as defined inclaim 23 wherein said microwave energy interactive material extendssubstantially over said food product.
 25. A microwavable package asdefined in claim 24 wherein said apertures are in the form of elongateslots.
 26. A microwavable package as defined in claim 25 wherein saidelongate slots are arranged in concentric circular rings, the slots inadjacent concentric rings being staggered.
 27. A microwavable package asdefined in claim 26 wherein microwave energy interactive materialislands are located within said elongate slots.
 28. A microwavablepackage as defined in claim 27 wherein said elongate slots are arrangedin concentric circular rings, the slots in adjacent concentric ringsbeing staggered.
 29. A microwavable package as defined in claim 28wherein each of said microwave energy interactive material islands hasan aperture formed therein.
 30. A microwavable package as defined inclaim 29 wherein said apertures are generally decussate.
 31. Amicrowavable package as defined in claim 23 wherein said base and activemicrowave energy heating element further include a plurality of spacedventing apertures to allow moisture released from said food product topass.
 32. A microwavable package as defined in claim 31 wherein saidventing apertures are arranged in concentric rings.
 33. A microwavablepackage as defined in claim 23 wherein said cover is flexible to overlieand conform to said food product, and further comprising a flexible wrapto constrain said base and cover and inhibit relative movement therebetween.
 34. A microwavable package as defined in claim 33 wherein saidbase and cover are generally circular.
 35. A microwavable package asdefined in claim 33 wherein said food product is in the form of a pizza.36. A microwavable package as defined in claim 1 further comprising: atray comprising said base and including a plurality of spaced aperturesin said tray to permit moisture released from a food product to passthrough said tray.
 37. A microwavable package as defined in claim 36wherein said apertures are arranged in concentric rings.
 38. Amicrowavable package as defined in claim 1 wherein the apertures arespaced about a peripheral margin of said cover.
 39. A microwavablepackage as defined in claim 23 wherein the apertures are spaced about aperipheral margin of said cover.